The number of deaths remains at 14, according to the U.S. Centers for Disease Control and Prevention.

All of the patients were thought to be injected with methylprednisolone acetate, a steroid drug often used for back pain that investigators suspect was tainted with a common fungus, according to the CDC.

The steroid was manufactured by a specialty pharmacy, the New England Compounding Center of Framingham, Mass., which last month voluntarily recalled three lots of the steroid. It has since shut down operations and stopped distributing its products, health officials said.

It's believed that as many as 14,000 people may have gotten the injections. Health officials in the 23 states that received shipments of the steroid have been able to contact about 11,000 patients, CDC officials said Thursday.

The 14,000 figure includes not only people who got injections for back pain and are most at risk for meningitis, but also others who received injections for pain in their knees and shoulders. Meningitis is inflammation of the lining surrounding the brain and spinal cord.

All of the infected patients are thought to have received the medication from the Massachusetts pharmacy, according to the CDC.

U.S. health officials said they expect to see more cases of the rare type of meningitis, which is not contagious, because symptoms can take a month or more to appear.

Infected patients have developed a variety of symptoms approximately one to four weeks following their injection. Symptoms include fever, new or worsening headache, nausea, and "new neurological deficit [consistent with deep brain stroke]," the CDC said.

Patients who have had a steroid injection since July, and have any of the following symptoms, should talk to their doctor as soon as possible: worsening headache, fever, sensitivity to light, stiff neck, new weakness or numbness in any part of your body, slurred speech.

Infected patients must receive intravenous drugs in a hospital.

Compounding pharmacies such as the New England Compounding Center combine, mix or alter ingredients to create specific drugs to meet the specific needs of individual patients, according to the U.S. Food and Drug Administration. Such customized drugs are frequently required to fill special needs, such as a smaller dose, or the removal of an ingredient that might trigger an allergy in a patient.

Compounding pharmacies historically started out as community-based neighborhood druggists. But over time, the practices of some compounding pharmacies have expanded, sometimes beyond their intended limits, experts explained.

According to the Associated Press, this is not the first time the New England Compounding Center has encountered problems with contaminated injections. In 2007, the company settled a lawsuit that claimed that an 83-year-old man died in 2004 after contracting fatal bacterial meningitis from a shot produced by the compounding center. The pharmacy reached a settlement with the man's widow before the case went to trial, the AP said.

The New England Compounding Center is relatively small, with 49 employees, The New York Times reported.

Compounding pharmacies aren't subject to the same oversight from the U.S. Food and Drug Administration as regular drug stores are, and members of Congress now say the meningitis outbreak highlights the need for more regulatory control.

"This incident raises serious concerns about the scope of the practice of pharmacy compounding in the United States and the current patchwork of federal and state laws," according to a statement by Rep. Henry Waxman, (D-Calif.) and two other Democrats on the House Energy and Commerce Committee, Rep. Diana DeGette of Colorado and Rep. Frank Pallone Jr. of New Jersey, the Times reported.

Rep. Edward Markey, a Massachusetts Democrat who represents the district that's home to the New England Compounding Center, said he would push for legislation that requires compounding pharmacies that distribute products across state lines to register with the FDA.